ios - mac - how to use audiobus 3

How does Audiobus for iOS work? (2)

My guess is that they use some sort of audio over network, because I've seen log statements when our app gets started even on a different device.

Don't really know about the details of the implementation, but this could be a way of staying in the "sandbox" constraint.

What SDK's does Audiobus use to provide inter-app audio routing? I am not aware of any Apple SDK that could facilitate inter-app communication for iOS and was under the impression that apps were sandboxed from each other so I'm really intrigued to hear how they pulled this off.

The Audiobus SDK (probably) use the Audio Session rules to "organize" all the sound output from the apps using their SDK, as you can see on their videos (on bottom of the page), the apps have an lateral menu to switch back and forwards between apps.

The Audio Session Category states:

Allows mixing: if yes, audio from other applications (such as the iPod) can continue playing when your application plays sound.

This way Audiobus can "control" the sound and allow the session to be persistent between the apps.